behavior among US adults. Cogent Soc Sci. 2017;3:1302785. https://doi.org/10.1080/23311886.2017.1302785 3. Piltch-Loeb R, Merdjanoff AA, Abramson DM. How the US population engaged with and prioritized sources of information about the emerging Zika virus in 2016. Health Secur. 2018;16:165–77. https://doi.org/10.1089/hs.2017.0107 4. Sell TK, Watson C, Meyer D, Kronk M, Ravi S, Pechta LE, et al. Frequency of risk-related news media messages in 2016 coverage of Zika virus. Risk Anal. 2018;38:2514–24. https://doi.org/10.1111/risa.12961 5. Wolfe JH. Pattern clustering by multivariate mixture analysis. Multivariate Behav Res. 1970;5:329–50. https://doi.org/10.1207/s15327906mbr0503_6 6. Goodman LA. The analysis of systems of qualitative variables when some of the variables are unobservable. Part IA modified latent structure approach. The American Journal of Sociology. 1974;79:1179–259. https://doi.org/ 10.1086/225676 7. Nylund KL, Asparouhov T, Muthén BO. Deciding on the number of classes in latent class analysis and growth mixture modeling: a Monte Carlo simulation study. Struct Equ Modeling. 2007;14:535–69. https://doi.org/10.1080/ 10705510701575396 8. Agarwal NK. Information source and its relationship with the context of information seeking behavior. In: iConference 2011: proceedings of the 2011 iConference; 2011 Feb 8–11; Seattle, Washington, USA. New York: Association for Computing Machinery; 2011. p. 48–55. Address for correspondence: Rachael Piltch-Loeb, New York University, Global Public Health, 715 Broadway Rm 1229, New York, NY 10003, USA; email: [email protected]Severe Fever with Thrombocytopenia Syndrome Virus in Ticks and SFTS Incidence in Humans, South Korea Jeong Rae Yoo, 1 Sang Taek Heo, 1 Sung Wook Song, Seung Geon Bae, Seul Lee, Sungho Choi, Chaehyun Lee, Sugyeong Jeong, Myeongseop Kim, Woojin Sa, Yeongrim Lee, Haseon Choi, Sun-Ho Kee, Keun Hwa Lee DOI: https://doi.org/10.3201/eid2609.200065 Author affiliations: Jeju National University, Jeju, South Korea (J.R. Yoo, S.T. Heo, S.W. Song, S.G. Bae, S. Lee, S. Choi, C. Lee, S. Jeong, M. Kim, W. Sa, Y. Lee, H. Choi); Korea University, Seoul, South Korea (S.-H. Kee); Hanyang University College of Medicine, Seoul (K.H. Lee). S evere fever with thrombocytopenia syndrome (SFTS) is a tickborne zoonosis caused by the SFTS virus (SFTSV) (1); >1,000 SFTS cases have been re- ported in South Korea (2). The SFTS prevalence rate was 2.26/100,000 inhabitants on the mainland and 13.66/100,000 inhabitants on Jeju Island, South Ko- rea (2). SFTSV has been detected in several species of ticks, including Haemaphysalis longicornis, Amblyomma testudinarium, and Ixodes nipponensis (3). A previous study reported that the minimum infection rate of SFTSV in infected ticks was lower (0.37%) on Jeju Is- land than in other collection areas (1.97%) (4). How- ever, 7%–14% SFTSV seropositivity was identified in domestic and wild animals (4–5), and 2%–5% SFTSV seropositivity was identified in a healthy population in South Korea (6). Therefore, our aim was to investi- gate the SFTSV infection rate (IR) in ticks in the region with the highest endemicity, Jeju Island, and to ana- lyze the relationship between the geographic distri- bution of ticks and SFTSV and human cases of SFTS. During June 2016–January 2019, well-equipped trained researchers collected ticks from the natu- ral environment of Jeju Island. The tick sampling sites included 5 rural areas: Aewol-eup (AW); Seon Hul-ri (SH); Jeo Ji-ri (JJ); and Ha Do-ri (HD) and Bo Mok-ri (BM) (Figure). These 5 areas were chosen to compare SFTSV IR in ticks in areas with the highest rates of human SFTS cases, SH, HD, and AW, and SFTSV IR in ticks in areas with lower human SFTS rates, JJ and BM. Ticks were manually collected 2 times per month, during the first and third weeks, by dragging a white cloth in woodlands for 2 hours in each area. We morphologically identified tick spe- cies and developmental stages by using an Olympus SD-ILK-200–2 stereomicroscope (Olympus Corpo- ration, https://www.olympus-lifescience.com) (7) and extracted viral RNA by using a QIAamp Viral RNA Mini kit (QIAGEN Inc., https://www.qia- gen.com) according to the manufacturer’s instruc- tions (Appendix, https://wwwnc.cdc.gov/EID/ article/26/9/20-0065-App1.pdf). 2292 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 26, No. 9, September 2020 RESEARCH LETTERS During 2016–2018, we collected 3,193 ticks from ru- ral areas in South Korea to investigate the prevalence of severe fever with thrombocytopenia syndrome virus (SFTSV). We detected SFTSV in ticks at an infection rate (IR) of 11.1%. We noted increases in the human IR as- sociated with the monthly SFTSV IR in ticks. 1 These authors contributed equally to this article.
Transcript
behavior among US adults. Cogent Soc Sci. 2017;3:1302785. https://doi.org/10.1080/23311886.2017.1302785
3. Piltch-Loeb R, Merdjanoff AA, Abramson DM. How the US population engaged with and prioritized sources of information about the emerging Zika virus in 2016. Health Secur. 2018;16:165–77. https://doi.org/10.1089/hs.2017.0107
4. Sell TK, Watson C, Meyer D, Kronk M, Ravi S, Pechta LE, et al. Frequency of risk-related news media messages in 2016 coverage of Zika virus. Risk Anal. 2018;38:2514–24. https://doi.org/10.1111/risa.12961
6. Goodman LA. The analysis of systems of qualitative variables when some of the variables are unobservable. Part IA modified latent structure approach. The American Journal of Sociology. 1974;79:1179–259. https://doi.org/ 10.1086/225676
7. Nylund KL, Asparouhov T, Muthén BO. Deciding on the number of classes in latent class analysis and growth mixture modeling: a Monte Carlo simulation study. Struct Equ Modeling. 2007;14:535–69. https://doi.org/10.1080/ 10705510701575396
8. Agarwal NK. Information source and its relationship with the context of information seeking behavior. In: iConference 2011: proceedings of the 2011 iConference; 2011 Feb 8–11; Seattle, Washington, USA. New York: Association for Computing Machinery; 2011. p. 48–55.
Address for correspondence: Rachael Piltch-Loeb, New York University, Global Public Health, 715 Broadway Rm 1229, New York, NY 10003, USA; email: [email protected]
Severe Fever with Thrombocytopenia Syndrome Virus in Ticks and SFTS Incidence in Humans, South Korea
Jeong Rae Yoo,1 Sang Taek Heo,1 Sung Wook Song, Seung Geon Bae, Seul Lee, Sungho Choi, Chaehyun Lee, Sugyeong Jeong, Myeongseop Kim, Woojin Sa, Yeongrim Lee, Haseon Choi, Sun-Ho Kee, Keun Hwa Lee
DOI: https://doi.org/10.3201/eid2609.200065
Author affiliations: Jeju National University, Jeju, South Korea (J.R. Yoo, S.T. Heo, S.W. Song, S.G. Bae, S. Lee, S. Choi, C. Lee, S. Jeong, M. Kim, W. Sa, Y. Lee, H. Choi); Korea University, Seoul, South Korea (S.-H. Kee); Hanyang University College of Medicine, Seoul (K.H. Lee).
Severe fever with thrombocytopenia syndrome (SFTS) is a tickborne zoonosis caused by the SFTS
virus (SFTSV) (1); >1,000 SFTS cases have been re-ported in South Korea (2). The SFTS prevalence rate was 2.26/100,000 inhabitants on the mainland and 13.66/100,000 inhabitants on Jeju Island, South Ko-rea (2). SFTSV has been detected in several species of ticks, including Haemaphysalis longicornis, Amblyomma testudinarium, and Ixodes nipponensis (3). A previous study reported that the minimum infection rate of SFTSV in infected ticks was lower (0.37%) on Jeju Is-land than in other collection areas (1.97%) (4). How-ever, 7%–14% SFTSV seropositivity was identified in domestic and wild animals (4–5), and 2%–5% SFTSV seropositivity was identified in a healthy population in South Korea (6). Therefore, our aim was to investi-gate the SFTSV infection rate (IR) in ticks in the region with the highest endemicity, Jeju Island, and to ana-lyze the relationship between the geographic distri-bution of ticks and SFTSV and human cases of SFTS.
During June 2016–January 2019, well-equipped trained researchers collected ticks from the natu-ral environment of Jeju Island. The tick sampling sites included 5 rural areas: Aewol-eup (AW); Seon Hul-ri (SH); Jeo Ji-ri (JJ); and Ha Do-ri (HD) and Bo Mok-ri (BM) (Figure). These 5 areas were chosen to compare SFTSV IR in ticks in areas with the highest rates of human SFTS cases, SH, HD, and AW, and SFTSV IR in ticks in areas with lower human SFTS rates, JJ and BM. Ticks were manually collected 2 times per month, during the first and third weeks, by dragging a white cloth in woodlands for 2 hours in each area. We morphologically identified tick spe-cies and developmental stages by using an Olympus SD-ILK-200–2 stereomicroscope (Olympus Corpo-ration, https://www.olympus-lifescience.com) (7) and extracted viral RNA by using a QIAamp Viral RNA Mini kit (QIAGEN Inc., https://www.qia-gen.com) according to the manufacturer’s instruc-tions (Appendix, https://wwwnc.cdc.gov/EID/article/26/9/20-0065-App1.pdf).
During 2016–2018, we collected 3,193 ticks from ru-ral areas in South Korea to investigate the prevalence of severe fever with thrombocytopenia syndrome virus (SFTSV). We detected SFTSV in ticks at an infection rate (IR) of 11.1%. We noted increases in the human IR as-sociated with the monthly SFTSV IR in ticks.
1These authors contributed equally to this article.
A total of 3,193 ticks were collected; most (99.9%) were H. longicornis and 81.3% of all ticks were nymphs. We detected SFTSV in 11.1% (354/3,193) of ticks (Ap-pendix Table). Among the 5 areas, the average IR of SFTSV in ticks was 12.8% in AW, 12.6% in SH, 12.0% in HD, 8.3% in JJ, and 7.8% in BM. Adult ticks had a higher SFTSV IR (12.4%) than nymphs (9.5%). SFTSV was detected mainly in adult ticks (Appendix Table).
The monthly IR of SFTSV in ticks increased in May, peaked in July, and then slowly decreased (Ap-pendix Figure 1). In addition, changes in the incidence of SFTS in patients were associated with increases in the monthly IR of SFTSV in ticks at a rate of 19.8% (95% CI 2.3%–40.2%) increase of SFTS in patients per 1% increase in monthly SFTSV IR in ticks (p = 0.02). SFTSV-infected ticks also were observed in the winter
season. SFTSV sequences from infected ticks in our study and SFTS patients on Jeju Island were consis-tent with each other but differed from viruses in other regions of South Korea (Appendix Figure 2).
In a previous study, the prevalence of SFTSV in ticks was very low (0.2%), implying that ticks alone might not be sufficient to maintain SFTSV in nature (8). However, the high IR of SFTSV in ticks could ex-plain why Jeju Island had one of the highest rates of human SFTS infection in South Korea. Changes in the incidence of patients with SFTS showed a pattern similar to that of monthly SFTSV IR in ticks. The IR of SFTSV in SH was the highest, along with HD and AW, where rates of human SFTS cases also were high.
In East Asia, humans most frequently acquire SFTS during May–July, and shrub, forest, and rainfed
Figure. Geographic distribution of patients with severe fever with thrombocytopenia syndrome (SFTS) during January 2013–January 2019 and yearly incidence rates of SFTS virus (SFTSV) from June 2016–January 2019 on Jeju Island, South Korea. Inset shows location of Jeju Island near the coast of South Korea. Orange indicate regions of patients with SFTS in 2013–2019. Graphs show SFTSV detected in ticks and cases of human SFTS in A) Jeo Ji-ri; B) Aewol-eup; C) Seon Hul-ri; D) Ha Do-ri; and E) Bo Mok-ri. AR, Ara-dong; AW, Aewol-eup; BG, Bonggae-dong; BM, Bo Mok-ri; DR, Daeryun-dong; GJ, Ganjeong-dong; GJW, Gujwa-eup; HB, Hwabug-dong; HD, Ha Do-ri; ILD, Ildo-dong; ID, Ido-dong; JC, Jocheon-eup; JJ, Jeo Ji-ri; NH, Nohyeong-dong; NW, Nanwon-eup; PS, Pyoseon-myeon; SHO, Seohong-dong; SH, Seon Hul-ri; SY, Samyang-dong; WP, Wolpyeong-dong.
cropland areas are associated with high risk for infec-tion(2,3,6). Northeast Jeju Island, which includes SH, AW, and HD, has many farms and wetlands, and the IR of SFTSV in ticks peaked there in July, August, and September. In addition, SFTSV was detected in ticks in winter on Jeju Island, but no SFTS cases were reported in South Korea during winter. The 62 confirmed SFTS cases were statistically significantly associated with higher ambient temperature (22.5°C +4.2°C) compared with patients with negative RT-PCR results for SFTSV (18.9°C +5.7°C; p<0.001) (J.R. Yoo, unpub. data). The optimal temperature range for growth and reproduc-tion of H. longicornis ticks is 20°–24°. Jeju Island main-tains a temperature >20° during May–October and is largely a rural and natural environment. We consider this area to have the highest prevalence of SFTS cases and ticks with SFTSV in South Korea.
The results of this study showed that Jeju Island has the highest IR of SFTSV in ticks compared with other regions of South Korea and endemic countries. In addi-tion, we found that the partial small segment of SFTSV in ticks was highly homologous to SFTSV in patients on Jeju Island and that Northeast Jeju Island, which in-cludes SH, is a high-risk area for human SFTS infections.
AcknowledgmentsWe thank the members of department of microbiology, Jeju National University, Graduate College of Medicine and the Safety for Agricultural Injuries of Famers cohort study, Jeju National University Hospital for assistance in collecting tick samples in various regions of Jeju Island, South Korea.
This work was supported by a grant from the Korea Health Technology Research and Development Project through the Korea Health Industry Development Institute and funded by the Ministry of Health & Welfare, South Korea (grant no. HG18C0037).
About the AuthorDr. Yoo and Dr. Heo are professors in the Department of Internal Medicine, Jeju National University, College of Medicine, Jeju, South Korea. Their research interests are infectious diseases.
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Appendix Table. Severe fever with thrombocytopenia syndrome virus detection in 3,193 ticks by developmental stage and region, Jeju Island, South Korea*
